The invention relates to a nuclear spin tomography method according to the preamble of patent claim 1. Such a method is described e.g. in U.S. Pat. No. 4,070,611.
Methods which permit the image-representation of the interior of bodies from the exterior pursuant to application of nuclear magnetic resonance effects have also become known under designations such as Zeugmatography, Spin-Imaging, Spin-Mapping or FONAR. With the aid of such methods it is possible to image the density of specific isotopes as well as the distribution of the nuclear magnetic relaxation times over a body cross-section. For medical diagnostics, the hydrogen bound to water is of particular importance. One can thus obtain, in a non-invasive manner, data regarding the physical and chemical state of living tissue. As the measuring basis for this purpose the known phenomena of nuclear magnetic resonance are employed.
In carrying out diagnostic methods of the present type, the body to be examined is exposed to a DC magnetic field B.sub.o and the nuclear isotopes to be be detected are excited to precession by means of a high frequency field B.sub.1. B.sub.1 must here have the frequency .omega.=.gamma..multidot.B.sub.o given by the gyromagnetic ratio. The allocation of the nuclear resonance signal--detectable in a receiver coil as a consequence of the precession movement--to the location of its origin proceeds through the application of linear magnetic field gradients, such as are described e.g. by P. C. Lauterbur in "Nature" 242 (1973), pages 190/191. If G.sub.x is the intensity of the field gradient in the x-direction, the local nuclear resonance frequency .omega. (x) results at: EQU .omega.(x)=.gamma.(B.sub.o +G.sub.x .multidot.x).
It is thus possible to allocate the nuclear resonance signal, on the basis of its frequency, to a specific location along the x-direction. Though successive application of linear field gradients G.sub.x, G.sub.y, and G.sub.z, in all three spatial directions x, y, z, also a three-dimensional localizing in an extended subject is possible.
A simple implementation of the method disclosed in the above-captioned U.S. Pat. No. 4,070,611 presents difficulties, since a very brief rise time of the gradient current pulses is required, on the one hand, and each virtually unavoidable basic field inhomogeneity leads to a reduction of the signal, on the other hand. The method described in the present invention is not, or only insignificantly, influenced by these two difficulties.